The skullcrusher is a tried-and-true triceps-targeted exercise you can perform with either a barbell or dumbbells. I see a lot of folks flare their elbows out as they perform each rep, which ends up placing a lot of stress on the elbow joint and connecting tendons—basically on areas other than the triceps
Keep your elbows steady and pointed toward your legs. The only motion occurring from this exercise should stem from the elbow joint, allowing your triceps to contract and work. Avoid locking out at the elbow at the top of the rep in order to keep constant tension on the triceps.